The kernel-joeghi-source package contains the source code files for the Mageia
kernel. Theese source files are only needed if you want to build your
own custom kernel that is better tuned to your particular hardware.
If you only want the files needed to build 3rdparty (nVidia, Ati, dkms-*,...)
drivers against, install the *-devel-* rpm that is matching your kernel.